Astronauts have been gardening on the International Space Station (ISS) for years to learn how plants grow in microgravity, with the idea that space crops will one day help sustain humans on long-duration missions such as to the Moon or Mars. Rather than resting in a soil garden bed, ISS plants grow in a pillow-like container that holds a ceramic growing medium with controlled-release fertilizer that provides nutrients over time. The pillow system is designed to be a passive watering apparatus but astronauts can also inject water directly as needed.
An LED lighting system enables the crew to grow crops independent of sunlight. Different light color combinations, or “light recipes,” can have dramatic effects on plant size, shape, texture, and appearance. Matthew Mickens, a NASA postdoctoral research fellow at Kennedy Space Center, investigates how different light recipes affect crop yield, as well as the nutrient content and flavor of plants.
The ISS crewmembers currently use three growth chambers for gardening: two simple Vegetable Production Chambers — more commonly referred to as Veggie units — and a newer plant growth system called the Advanced Plant Habitat (APH), which joined the space station’s Veggie units in the fall of 2017 and was initiated in January 2018.
Like the earlier growth chambers, the APH secures seeds in a growing medium; however, unlike the Veggie units, APH allows users to exercise complete control of the plant’s environment. At about the size of a mini-fridge, it’s larger than the Veggie units. It’s more automated as well, with many functions driven by a computer on board, minimizing the amount of time astronauts have to spend gardening.
APH has an improved custom-designed LED system that offers a greater variety of light colors and intensities. The Veggie habitats are equipped with red, green, and blue LEDs, while the APH adds white and far-red, a light color between red and infrared barely visible to the human eye but detected and used by plants.
Controlling light for crop growth is also a terrestrial horticultural focus where there is growing interest in vertical farming — techniques enabling food and other crops to be grown indoors in places like skyscrapers. OSRAM — a German lighting company with U.S. headquarters in Wilmington, MA — has been working on a horticulture lighting solution to improve research in this field through a project headed by Steve Graves, strategic program manager for urban and digital farming in the company’s innovation group.
The OSRAM solution, Phytofy RL, is a tray-like fixture with a network of LED lights, temperature control, and a software-controlled panel to adjust settings. Aware of both NASA’s plant projects and OSRAM’s technology, vertical farming specialist Chris Higgins, founder of Hort Americas (a company that works with commercial greenhouse growers), introduced the Kennedy researchers to OSRAM’s developers in 2017. Later that year, Mickens began using a Phytofy prototype provided by OSRAM to conduct ground-based studies for in-space APH experiments. Mickens and the OSRAM team installed the Phytofy in a reach-in growth chamber and eventually plan to use the lighting fixture in Kennedy’s walk-in growth chambers as well. Mickens says OSRAM’s device offers choices in light wavelength, which determines light color, similar to the APH.
OSRAM is initially marketing a Phytofy solution to plant scientists that features a configurable lighting system with realtime controls as well as scheduling capabilities. Graves expects future versions will add automation and sensor options to help reduce the large amount of human observation that plant science now requires. All settings can be controlled through a graphical user interface.
OSRAM has designed Phytofy’s current light spectra — light wavelength (color) and intensity — specifically for researching plant light recipes, including the farreds that mimic end-of-day sunlight, brief UV light, and night interruption light that can also affect how plants grow.
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